The invention relates to welding electrodes for manual arc welding under water.
Modern techniques of metallic construction, as well as the corresponding ones of conversion and repair, often require welding operations in the most varied working conditions, particularly underwater welding operations. Of these operations, those for which the arc is put directly into the water (wet welding) require the minimum of immersed equipment. Their potential field of application is wider and they can be carried out at a lower cost than in the case of hyperbaric welding.
As is known, the underwater use of welding electrodes often meets with difficulties which are peculiar to this kind of application and which generally allow only a relatively poor quality of weld deposit. Of these disadvantages, particular mention may be made of the cracking of the weld deposit, which cracking is essentially caused by the presence of hydrogen resulting from the decomposition of the water by the electric arc in the immediate vicinity of the part of the weld which is being deposited. This hydrogen has a strong tendency to become occluded in the deposited metal, thus making it particularly susceptible to cracking.
The electrodes which are currently commerically available for underwater welding generally comprise a coating with a rutile base. It is therefore possible to keep the arc quite stable and to obtain a well-formed deposit. However, as mentioned above, this kind of coating has the disadvantage of introducing a high hydrogen content into the deposited metal. There is therefore a considerable risk of cracking, which may cause the joint to be ruined.
There have also been attempts to carry out this kind of underwater welding, in a semi-automatic manner, by injecting an inert gas under pressure so as to maintain a protective atmosphere around the welding spot, which is not detrimental to the deposited bead. It seems that even this technique has failed to produce results which might be considered satisfactory, particularly because of operational difficulties.
Tests which we have carried out have shown that a coating of the oxidizing type enables one to reduce the hydrogen content in the molten metal, and therefore the risk of cold cracking. This is illustrated below in Tables I and II.